A closer look at the numbers, though, reveals a gender divide — with young women making economic strides and young men falling behind.

The percentage of young men in the U.S. workforce has not shifted much from just under 85 percent in 1975. But the share of young women working full time has jumped from just shy of one-half (49 percent) to more than two-thirds (70 percent) over the past four decades. And more of them are moving into higher income brackets: The share of young women earning $60,000 or more (in 2015 dollars) increased from around 2 percent to 13 percent.

In fact, young female workers have been driving the growth of the young workforce in the U.S. since 1975.

Their male counterparts, on the other hand, appear to be on the economic decline.

"They are falling to the bottom of the income ladder," says Jonathan Vespa, a demographer at the Census Bureau who wrote the report.

The share of young men making less than $30,000 a year, he writes in the report, has "swelled" from 25 percent in 1975 to around 41 percent in 2016. There have also been a drop in the share of young men making $30,000 to $59,999 — from almost half (49 percent) to more than a third (35 percent).

"It is little surprise then that those still living with parents are disproportionately young men," writes Vespa, adding that today young men are more likely to be idle — not in school and not working — than 40 years ago.

Despite these shifts, a gender gap in young men's favor remains. While young women have seen a $6,000 jump in their median income (from $23,000 to $29,000), it is still $11,000 lower than the median income of young men.